Monitoring the status of an individual's physical condition with the help of various external sensors is of general interest. Of particular relevance is the measurement of parameters such as heart rate, pulse-shape, brain activity, blood pressure, or blood glucose content. The onus on the designers looking to design such a sensor is that the sensor must provide maximum functionality without hindering the user mobility by any significant degree. This has led to the evolution of the concept of “electronic skin,” a stretchable flexible polymer foil which can be attached to skin and which can incorporate all the essential electronics required for a specific purpose, or even multiple purposes. Fundamental to the success of developing such a sensor is the advancement of stretchable (bio)electronics. This involves the development of electronic devices that retain good functionality even under stretching.
To date, several strategies have been attempted to address this issue. One such strategy has been to exploit novel composite materials. This involves the incorporation of conductive filler materials, such as metal nanoparticles, metal nanotubes, graphite, carbon nanotubes (CNTs), and conducting polymers, into a rubbery polymer matrix through blending. Composites designed for stretchable electronics have attracted increasing attention in recent years because they are potentially more mechanically durable and are more promising for large-scale applications. Current state-of-the-art demonstrations have shown that composites with very high conductivities can be prepared (≥103 S/cm) and that the composites maintain such high conductivities even at very large strains (≥100%). However, there exists a limit to this strategy, as the incorporation of high concentrations of conductive fillers, such as CNTs, into the polymer matrix to increase conductivity can result in the decrease of the stretchability of the resultant composite. Also, many nanomaterials are too expensive for most practical applications.